The present invention relates to a driving control apparatus for an industrial vehicle that includes a torque converter between an engine and a transmission.
Japanese Unexamined Patent Publication No. 10-151974 discloses an industrial vehicle that includes a torque converter between an engine and a transmission. The torque converter has an input shaft, which is coupled to the engine, and an output shaft, which is coupled to the transmission. The torque converter continuously varies the rotational ratio between the input shaft and the output shaft in accordance with the load on the output shaft. The torque converter and the transmission form an automatic transmission.
The vehicle of the publication does not include a clutch pedal. Basically, the vehicle is controlled by manipulating an acceleration pedal, a brake pedal and a shift lever for changing the moving direction of the vehicle. Since the vehicle has no clutch pedal, an operator need not actuate a clutch pedal, which requires subtle manipulation. The vehicle can be therefore easily operated by an inexperienced operator.
Compared to ordinary passenger cars, a typical industrial vehicle such as a forklift receives a great load on the wheels. Therefore, skidding of the wheels due to acceleration or braking wears the wheels and marks the road surface.
To avoid such disadvantages, traction control and anti-lock brake control, which have been used for ordinary passenger cars, may be used for industrial vehicles. This will prevent the wheels from spinning when the vehicle is accelerating and from locking when braking the vehicle. Hereinafter, traction control will be referred to as TRC control and anti-lock brake control will be referred to as ABS control. TRC control and ABS control, together with an automatic transmission, facilitate driving of industrial vehicles.
However, systems for TRC control and ABS control for ordinary passenger cars include multiple sensors for detecting skidding of wheels such as a sensor for detecting the speed of driving wheels and a sensor for detecting the speed of driven wheels. Further, the system needs many other special devices such as an actuator for controlling the braking force, which increases the cost. Unlike ordinary passenger cars, an industrial vehicle runs at twenty kilometers per hour at a maximum and is used in a different environment and different conditions. Thus, considering the cost and the suitability, TRC control and ABS control for ordinary passenger cars cannot be used in industrial vehicles without adjustment.
Some types of forklifts that have an automatic transmission can perform direction switching. Direction switching refers to switching a shift lever while the vehicle is running for switching the moving direction of the vehicle. Direction switching permits the vehicle to start moving in a direction that is opposite to the current moving direction after temporarily stopping without manipulating a brake pedal.
During the direction switching, the wheels must be stopped without being locked and then must be started in the opposite direction without spinning. Therefore, there is a demand for an inexpensive system that reliably prevents wheels from skidding when the moving direction is switched.
Accordingly, in an industrial vehicle that uses an automatic transmission, it is an object of the present invention to provide a driving control apparatus that performs TRC control and ABS control, which are suitable for industrial vehicle, thereby preventing the wheels from skidding with a simple structure.
To achieve the foregoing and other objectives, the present invention provides an industrial vehicle including an engine, a torque converter, a transmission coupled to the engine by the torque converter, and a driving wheel. The driving wheel is rotated by power that is transmitted from the transmission. A hydraulic brake brakes the driving wheel. The hydraulic brake generates a braking force, the magnitude of which corresponds to a hydraulic pressure applied to the hydraulic brake. A brake valve adjusts the hydraulic pressure applied to the hydraulic brake. A brake actuator is moved by a human operator to actuate the hydraulic brake. A sensor detects the rotational speed of the driving wheel. A controller controls the brake valve such that the hydraulic brake brakes the driving wheel with a force of a normal value, which corresponds to a force applied to the brake actuator. The controller computes the rotational deceleration of the driving wheel while braking based on the detected rotational speed. When the computed rotational deceleration exceeds a predetermined deceleration determination value, the controller controls the brake valve such that the braking force of the hydraulic brake is set to a limit value, which is smaller than the normal value.
The present invention also provides an industrial vehicle including an engine, a torque converter, a transmission coupled to the engine by the torque converter, and a driving wheel. The transmission includes a forward clutch, which is engaged when the vehicle is moving forward, and a reverse clutch, which is engaged when the vehicle is moving backward. The driving wheel is rotated by power that is transmitted from the transmission. A sensor detects the rotational speed of the driving wheel. A controller controls the engine and computes the rotational acceleration of the driving wheel when the vehicle is accelerating based on the detected rotational speed. When the computed rotational acceleration exceeds a predetermined acceleration determination value, the controller controls the engine output to limit the power transmitted to the driving wheel.
The present invention also provides an industrial vehicle having an engine, a torque converter, a transmission coupled to the engine by the torque converter, a forward clutch valve, a reverse clutch valve and a driving wheel. The transmission includes a hydraulic forward clutch, which is engaged when the vehicle is moving forward, and a hydraulic reverse clutch, which is engaged when the vehicle is moving backward. Each clutch produces an engaging force, the magnitude of which corresponds to a hydraulic pressure applied to the clutch. The forward clutch valve controls the hydraulic pressure applied to the forward clutch. The reverse clutch valve controls the hydraulic pressure applied to the reverse clutch. The driving wheel is rotated by power that is transmitted from the transmission. A sensor detects the rotational speed of the driving wheel. A controller controls the clutch valves and computes the rotational acceleration of the driving wheel when the vehicle is accelerating based on the detected rotational speed. When the computed rotational acceleration exceeds a predetermined acceleration determination value, the controller decreases an engaging force of one of the clutches that corresponds to the moving direction of the vehicle for decreasing the power transmitted to the driving wheel by controlling the corresponding clutch valve.
The present invention further provides an industrial vehicle having a drive source, a differential, and a pair of driving wheels coupled to the drive source by the differential. The differential permits the rotational speeds of the driving wheels to differ. A brake for brakes the driving wheels. A skid detector detects skid values, each representing the degree of skidding of one of the driving wheels. A controller controls the drive source or the brake for eliminating skidding of the driving wheels based on the greater of the detected skid values.
The present invention yet further provides an industrial vehicle having an engine, a torque converter, a transmission coupled to the engine by the torque converter, a differential, and a pair of driving wheels. The transmission includes a hydraulic forward clutch, which is engaged when the vehicle is moving forward, and a hydraulic reverse clutch, which is engaged when the vehicle is moving backward. Each clutch produces an engaging force, the magnitude of which corresponds to a hydraulic pressure applied to the clutch. The driving wheels are coupled to the transmission by the differential. The differential permits the rotational speeds of the driving wheels to differ. A skid detector detects skid values, each representing the degree of skidding of one of the driving wheels. A controller controls the clutches. When the greater of the detected skid values exceeds a predetermined acceleration determination value while the vehicle is accelerating, the controller decreases the engaging force of one of the clutches that corresponds to the moving direction of the vehicle for decreasing the power transmitted to the driving wheels.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.